For the statistic, choose one of the statistics (for example, Average) or
predefined percentiles, or specify a custom percentile (for example, p95.45).

Choose a period (for example, 1 Hour).

Choose Next.

For the Define Alarm step, do the following:

Under Alarm Threshold, type a unique name for the alarm and a
description of the alarm. The alarm name must contain only ASCII characters. For
Whenever, specify a threshold (for example, 80 percent of CPU
utilization) and the number of datapoints ("M" out of "N") that must be breaching
to trigger the alarm. For more information, see Evaluating an Alarm.

If the alarm uses a percentile as the monitored statistic, choose whether to
evaluate or ignore cases with low sample rates. If you choose
ignore, the current alarm state is maintained when the sample
size is too low. For more information, see Percentile-Based CloudWatch Alarms and Low Data Samples.

Under Actions, select the type of action to have the alarm to
perform when the alarm is triggered.